Remote sensing devices may be used to detect and characterize emissions from a vehicle. One device for performing such a process analyzes radiation that passes through the vehicle emission using a detector. Various components of the vehicle emission absorb radiation of specific characteristic wavelengths. A filter is used to permit only a radiation band including the characteristic wavelength of interest to reach the detector. If multiple components of the emission are to be analyzed in this manner, multiple sets of detectors and filters are generally necessary to carry out such measurements.
A known device for the remote sensing of vehicle emissions is depicted in FIG. 1. A beam (1) from a radiation source (7) passes through emissions plume (8) of vehicle (9) and is reflected from mirror (2) onto reflecting wheel (3). Beam (1) is then reflected from reflecting wheel (3) to one of a group of CD mirrors (4). The group of mirrors (4) focus and reflect the beam (1) through respective filters (5) and onto respective detectors (6). One such remote sensing device is disclosed in U.S. Pat. No. 5,210,702.
Such devices, however, may have certain drawbacks. These devices may have a large number of parts to manufacture, assemble, align, maintain, and calibrate, including special reflectors, multiple detectors and multiple light filters. Each of these parts introduces error into the final measurements. For example, light filters may suffer from light bleed, allowing undesirable wavelengths of light to reach the detectors. Uncertainty as to the measurements may also occur because different detectors may react differently to the variety of conditions encountered during the use of these devices.
Additionally, use of multiple filters, detectors, reflectors, and the like can add considerable complexity and bulk to the device. Also, if other components of the emission are to be detected, the replacement of filters and/or detectors to provide suitable filters and detectors for such other components may involve considerable cost in parts, as well as in assembly, alignment, and calibration of the device.
Another gas analysis device is disclosed in U.S. Pat. No. 4,678,914. This device employs an infrared (IR) gas analyzer in which IR radiation from a source is directed toward an IR detector. The IR radiation passes through both a gas located in a sample cell and then one of various light filters mounted on a continuously rotating filter wheel. This device requires close proximity to an emissions output in order to operate properly, and employs a sample chamber for gas analysis. Devices which employ a gas sample chamber are not feasible for remote sensing of vehicle emissions because of the need to collect a sample of the emission and isolate it in the gas sample chamber. Also, such devices only provide a localized reading of the gas at the exact point where the sample is taken.
These and other drawbacks of known devices exist.